Yep, the trucks on this particular car do swivel 360 degrees. With that in mind, I can see that if it were any lower, the trucks would hit the bottom of the ladders that hang down below the level of the platform. Wow, 3x the length of my longest car! If I went by that rule, I'd only have room for about half of my layout!
As I said, the 3X is a conservative standard that allows for full underbody detail, prototype height of underframe, and body-mounted couplers. If you use the 3X standard, you won't see stringlining or other derailments caused by curve radius. In most cases, 2.5X is pretty reliable, but personally I would want to be at 3X on critical trackage - hidden or helix or similar.
In narrow gauge because wheels often were located between underframe beams or other items, sometimes an accurate model will struggle at a 3X radius. In N where truck-mounted couplers are the norm, 2 to 2.5X is usually sufficient.
Not that none of this addresses appearance on curves. The NMRA RP 11 (
NMRA RP-11 Curvature & Rolling Stock) has similar recommendations broken down into class as well as length of locomotives and rolling stock.
Can you get away with smaller radius? Absolutely! But the further you stray from the recommendations, the more likely a long piece of rolling stock is going to struggle on your curves and require modifications to run reliably.
Personally, I will never have the room for more than about 22" radius curves in HO. But because my space is small, modern long rolling stock and locomotives look silly to me, anyway. So I'm quite content with the 1900-era, when railroading dreams were huge, the rolling stock and locomotives were small, and narrow gauge was still practical.
yours in having fun